Official United Nations Chagall Window Envelope with 6c stamps series. Stamped November 17, 1967 with the United Nations Seal, New York - Fist Day of Issue. Official WFUNA Cachet. Entire 6-stamp series with the entire Chagall Window scene. Never addressed, still in original pouch, and comes with a certificate of authenticity. Extremely rare. Very small crease on bottom right corner.